A. Technical Field
The present invention relates generally to measurement and testing and, more particularly, to a method and apparatus for sensing dimensional or position measurements in response to light intensity directed toward a photosensitive cell.
B. Background Art
Previously known methods and apparatus used for sensing dimensional conformity of workpieces in industrial environments have been available for quality control, but only at great cost to the manufacturers. Dimensional inspection and testing of manufactured component parts has been accomplished by removing the component during various stages of manufacturing on a sampling basis and checking it dimensionally using a specialized checking fixture and in some instances a coordinate measuring machine. More recently, inspection and testing is desired in the production line, and by checking the component at various stages within the manufacturing process, each piece produced can be tested. In both cases, industrial probes also known as gauges are used in conjunction with the work holding device to accomplish the measurement.
For the most part, the previous probes were typically contact probes in the form of dial type indicators. Such indicators employ a spring-loaded stylus which is displaced through a measuring range by engagement with the workpiece and accordingly, moves a dial indicator as the part is engaged by the stylus. Alternatively, movement of the stylus relative to the probe housing may produce an electrical or electromagnetic reaction. For example, electrical resistance varies with movement of the stylus in U.S. Pat. No. 4,651,623.
More recent developments have sought to incorporate machine vision or other non-contact probes to check workpieces during the production process. However, the known photo-optical technology requires complex light focusing sources as well as complex arrays of sensors and computer software to analyze the numerous sensor signals. These gauging systems may employ optical sensors which are known to provide an output directly corresponding to changes in the illumination intensity impinging upon the sensor, such as photovoltaic cells. However, the previously known applications involve complex optical circuits and, despite the complexity and expense of the circuitry and system, may often have a very limited utility in manufacturing.
Non-contact probes have also been known to generate changes in a magnetic field resulting from the proximity of a workpiece to a probe housing. However, these changes are not well-suited to an industrial environment because numerous environmental equipment and the workpieces themselves may influence the magnetic fields and interfere with accurate electromagnetic responses.
In today's manufacturing environment, both the contact and the non-contact probes must feed back analog or digital data to an analyzer or computer.
Defensive publication 702,459 and U.S. Pat. No. 3,005,916 disclose apparatus for photoelectrically scanning moving surfaces to detect the presence of irregular surface configurations in the form of protrusions or indentations on a planar surface. Numerous components are required to particularly focus a light source from one predetermined direction and receive the reflected light from another direction. However, both the aligned source and receptor create shadows which occur only when the workpiece surface is at a particular distance from the focusing apparatus. The device would be inoperable if the distance to the workpiece changed, and the system response is unrelated to the measurement of distance from the sensor.
U.S. Pat. No. 3,591,291 discloses a surface roughness detector in which a light beam from a source is collimated by appropriate lenses to direct the beam against the surface to be tested. The sensor housing is engaged against the workpiece surface so that reflections can be detected by a series of discretely positioned light sensitive element arranged at different predetermined angles within the housing. Any variation of the distance between the sensor housing and the workpiece interferes with the illumination intensity reflected to the light sensitive elements. As a result, the apparatus is not adapted to measure distances between the sensor and the workpiece.
U.S. Pat. No. 3,571,579 also discloses a previously known device for detecting irregularities in the surface of a workpiece. However, the irregularities are detected by a stylus which engages the workpiece and reacts to movement of the workpiece. Such contact with the workpiece and relative movement between the stylus and the workpiece can cause damage to the surface. The stylus movement is used to generate signals representative of the irregularities which can be optically stored by recreation on a storage medium such as a film strip or magnetic tape. The film strip recording is then examined by a plurality of photosensitive devices to determine the signal characteristics generated and for subsequent analysis.
Apparatus using photosensitive devices used to detect dimensional characteristics are extremely complicated. For example, U.S. Pat. No. 4,666,303 to Pryor discloses an electro-optical gap and flushness sensor that utilizes a laser light source to provide a highly directionalized source of light and focusing lenses to direct the light beam to the part surface to be tested. Moreover, the light reflected from the workpiece is refocused to form an image on a photo detector array. The photo detector array comprises a plurality of photosensitive cells, and the numerous cell outputs are then analyzed by a microcomputer using triangulation equations to determine the dimensional characteristics of the workpiece surface. While such a system may be fairly accurate, the complexity of the illumination sources and the detecting apparatus renders such systems extremely expensive.